Control device, device for fixing a stack of paper sheets and unstacking device

ABSTRACT

The invention relates to a control device for the removal of a partial stack from a stack of paper sheets comprising a camera ( 30 ) for generating of a camera image, means ( 41 ) for generating of at least two substantially parallel light beams whose reflections ( 52, 53 ) on the stack of paper sheets are reproduced in the camera image ( 50 ), and means providing a control signal for the removal of a partial stack ( 12 ) using the distance ( 54 ) of the reflections ( 52, 53 ) in the camera image ( 50 ). 
     Furthermore, the invention relates to un unstacking device for the removal of a partial stack from a stack of paper sheets, comprising a parting mechanism ( 20 ) with a parting knife ( 21 ), wherein the parting knife ( 21 ) can be swivelled upwards and/or downwards in order to be able to follow the paper progress upwards and/or downwards during unstacking.

1. TECHNICAL FIELD

The present invention relates to a control device for the removal of a partial stack from a stack of paper sheets, a device for fixing a stack of paper sheets, and an unstacking device.

2. THE PRIOR ART

At the processing of paper a stacking and palletizing is often carried out after the production. At the further processing partial stacks have to be generated which contain a predetermined number of paper sheets as exactly as possible. For this purpose, for example gripping devices are used which remove a partial stack from the complete stack.

For this purpose, it is known from EP 1 264 792 that paper of a certain quality has a uniform thickness. Paper stacks of the same quality only differ in their height, if there are air gaps between individual sheets. Therefore for de-stacking, it is known to compress the paper on one side with a certain contact pressure per unit area resulting reliably in stacks of an identical height for the same number of sheets and the same paper quality. To separate a ream with a predetermined number of sheets, it is plunged into the paper stack from the top edge at a certain height given by the predetermined number of sheets, and thus separating the above ream of the predetermined number of sheets from the remaining residual blank stack.

Therefore, it is a prerequisite of this method that the stacked paper has a uniform thickness. In reality the thickness of the paper may vary during different production runs. To determine nevertheless a number of paper sheets to be removed as exactly as possible, a method is known in which the number of paper sheets is counted by means of a picture recorded with a camera. For this purpose a camera picture is analyzed and the height of the desired number of paper sheets is determined from the picture. If the distance of the stack of paper sheets from the camera is known the corresponding plunge position for the unstacking device can be calculated.

The described prior art has several disadvantages: By using a contact pressure per unit area having the objective to obtain as exactly as possible the height of the paper stack to be removed corresponding to its number of paper sheets, there is the danger that the paper sheets are damaged when the parting knife penetrates into the stack.

Furthermore, all paper sheets have the same distance at each position of the image plane, only if the side of the stack of paper sheets facing to the camera is perpendicular to the axis of the camera. In practise, this condition is often not fulfilled leading to errors and inexactnesses when calculating of the plunge position for the partial stack to be removed.

In this context further devices known from the prior art are disclosed in the DE 1 013 156, DE 102 60 712 B3, DE 10 2004 044 341 A1, DE 40 34 339 A1, DE 35 08 514 A1, DE 28 49 949 A1, EP 1 584 584 A1 and EP 0 173 613 B1.

The present invention is therefore based on the problem to control as exactly as possible the removal of a partial stack of paper sheets and not to damage the paper sheets or to damage the paper sheets to the least possible extent.

3. SUMMARY OF THE INVENTION

This problem is solved according to a first aspect of the invention by a control device for the removal of a partial stack from a stack of paper sheets having a camera for the generation of a camera image, means to generate at least two substantially parallel light beams whose reflections are reproduced on the stack of paper sheets in the camera image, and means which provide a control signal for the removal of the partial stack using the distance of the reflections in the camera image. In a preferred embodiment the light beams extend substantially parallel to the plane of the paper sheets.

The control device according to the invention for the removal of a partial stack is based on a fundamentally different principle for determining the plunge point for the partial stack, or for other parameters than the methods known from the prior art, since the determination is independent from the distance of the stack of paper sheets from the camera and does not presume that the side of the stack of paper sheets facing to the camera is perpendicularly aligned to the camera axis. If the light beams are substantially parallel the number of paper sheets between the light beams is independent from the distance of the stack of paper sheets to the camera. The reflections of both light beams on the stack of paper sheets define a predetermined distance which can be used to convert any parameter of the camera image in other units of measurement. This is not only beneficial for the removal of a partial stack, but also for other applications at the processing of paper.

The same result can also be obtained without parallel lasers by a telecentric lenses. With such an objective no parallax errors can arise from an inexact distance between camera and paper.

According to a further aspect, the present invention relates to a device for fixing of a stack, in particular of a partial stack of paper sheets having means for inserting of electrostatic charge into a stack of paper sheets. A stack of paper sheets can be fixed by this device without the need to apply a contact pressure per unit area, as it is necessary according to the methods of the prior art so that mechanical damages of the stacked paper sheets can largely be avoided.

Finally, the present invention relates to an unstacking device having the mentioned device for fixing a stack of paper sheets and/or having the mentioned control device for the removal of a partial stack from a stack of paper sheets. Such an unstacking device does not only enable a highly precise removal of a partial stack, but also a substantially free of damage removal of a partial stack.

Preferably, the unstacking device has a parting mechanism and a parting knife as well as preferably a lifting device for the stack of paper sheets which lowers the residual blank stack after a broaching with the parting knife. For this purpose, the parting knife is preferably formed in a manner so that it can be swivelled down-ward when the residual blank stack lowers. This procedure has the advantage that the parting knife does not substantially damage the paper sheets lying above the parting knife when the residual blank stack lowers. Preferably, the parting knife is swivelled downward in such a manner that it is adjusted substantially parallel to the residual blank stack lying above.

Additionally to the described possibility to swivel downward, the knife has also the possibility to swivel upward. This enables a free of damage plunge into a stack whose paper sheets are inclined upward or downward.

With the explained unstacking device, the paper sheets stacked above the parting knife are preferably not loaded from the top during any phase of the removal of the partial stack of paper sheets. Compared with the application of a contact pressure per unit area, the damages of the paper sheets are minimized when the parting knife penetrates into the stack of paper sheets.

4. SHORT DESCRIPTIONS OF THE DRAWINGS

In the following detailed description presently preferred embodiments of the invention are described with respect to the following figures:

FIG. 1: Schematic side view of a preferred embodiment of an unstacking device according to the invention;

FIG. 2: Schematic side view of a camera image of the camera from FIG. 1;

FIG. 3: Schematic side view of a further preferred embodiment of an unstacking device having means for inserting of electrostatic charge.

5. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following presently preferred embodiments of the present invention are described with respect to an unstacking device. However, it is appreciated that the control device according to the invention and the device for fixing of paper sheets can also be applied in other contexts for the processing of paper stacks.

FIG. 1 is a schematic side view of an unstacking device. From FIG. 1 it can be seen a parting mechanism 20 with a parting knife 21 removing a partial stack 12 of paper sheets from a residual blank stack 11. In front of the stack of paper sheets, there is a camera 30 recording an image of the stack as well as means to generate light beams 41, 42, preferably laser beams which are required for a control of the unstacking device described in the following.

To remove as precisely as possible the desired number of paper sheets from the stack of paper sheets, the desired number of paper sheets is initially counted via a camera image of the stack recorded by the camera. An image processing software analyzes the recorded camera image on a suitable processing unit, for example a personal computer and determines the height of the desired number of paper sheets. To really remove the counted number of paper sheets by a suitable parting mechanism, it is necessary to convert the determined plunge position in the camera image to an absolute position for the parting mechanism 20. Only by this means, it is secured that the parting mechanism 20 is inserted at the correct position into the stack to remove the desired number of paper sheets for a partial stack.

As it is depicted in FIG. 1, for this purpose two (or more) light beams, preferably laser beams are used whose reflections 52, 53 are reproduced in the camera image (cf. FIG. 2). The light beams are substantially parallel to the plane of paper sheets whereby the number of paper sheets between the light beams is independent from the distance of the stack of paper sheets to the camera. By detecting the known distance of the light beams in the camera image (cf. FIG. 2), it is possible to convert the plunge position in the camera image independent from the distance of the paper sheet to the camera to a unit of measure used by the parting mechanism 20, e.g. micrometer. Deformations of the stack, as for example an inclined standing compared with the camera image can be balanced. This enables a higher accuracy when unstacking paper sheets.

FIG. 2 is a schematic view of a camera image 50 of the camera 30 from FIG. 1 with a partial stack of paper sheets 51 and two reflections 52, 53 of light beams. The distance 54 of the reflections 52, 53, that is the length of the connection line of the two reflections can be measured in the camera image 50, for example in units of pixel of the camera image and can be compared rationally to the effective known distance of the two light beams. Thereby, any parameters in the camera image can be converted into absolute distances or areas. This is not only beneficial for the removal of a partial stack, but it is also beneficial for other applications at the processing of paper.

For example the height 55 of a partial stack measured in pixel can be converted into the unit of measure of the known distance of the light beams, e.g. micrometer. For the calculation of a control signal for the parting mechanism 20, it is furthermore preferred to define an absolute reference point of the parting mechanism 20 in the camera image 50.

It is furthermore beneficial if the distance of the paper sheets to the camera is known. A measurement of the distance can be done for example by triangulation. For this purpose, a further laser beam 42 is used which is in a certain angle, preferably not parallel to the camera axis 31 (cf. FIG. 1).

The device presented in FIG. 1 is used to separate exactly and without any damage the predetermined number of paper sheets determined by the camera 30 in the explained manner. It has a lifting device (not shown), preferably a servo-controlled lifting device with highly precise ball spindles free of play as well as a parting mechanism 20 with a parting knife 21. The plunge position determined by the camera 30 is exactly set with the lifting device. Then the parting knife 21 is exactly inserted into the stack at this position.

The provisions described in the following are preferred so that no damage occurs at the paper. The parting knife 21 has preferably exactly in the axis of the knife an air nozzle (not shown) which spreads the paper exactly at the plunge position by means of an air jet. The parting knife 21 is further preferably formed so that it can be swivelled upward and downward to be able to follow the paper progress upward and downward. The parting knife 21 is then inserted at this position into the stack with very low strength. In doing so, in a first step the stack is only slightly broached. To enable a broaching of the stack without damage in each phase of the process, the paper sheets above the parting knife 21 should preferably not be loaded from the top. In a second step the stack of paper sheets is driven downward to a certain extend by a further lifting device. Thus, the free space between the partial stack 12 to be removed and the residual blank stack 11 lying below is increased and the parting knife 21 can be further introduced in the stack.

In order that also at this process step no damage occurs at the paper, further air is blown into the free space by the air nozzle described above for a suitable time period. It is additionally preferred that the parting knife 21 can further penetrate into the stack of paper sheets with very low strength. To enable this, the paper above the knife is preferably not loaded from the top in any phase of the process. In a particularly preferred embodiment, the parting knife 21 swivels downward by a suitable angle α. This ensures that the paper sheet or the paper sheets directly above the parting knife 21 are not damaged by the knife point. Preferably, the parting knife 21 is swivelled downward by such an angle α that it is substantially parallel to the lower side of the partial stack 12 which contacts the parting knife 21.

FIG. 3 is a side view of a device for fixing paper sheets which has means for inserting of electrostatic charge 60 into the stack of paper sheets. During counting of the paper sheets and the following parting cycle, the paper sheets to be removed have to be precisely positioned and fixed in a predetermined position. However, paper sheets, for example highly calendered paper adhere only poorly on each other. An unintended displacement of paper sheets stacked on each other can therefore only be avoided by contact forces which are provided in the prior art by a compression of the sheets. But every mechanical load causes undesired markings at the paper sheet. With the device shown in FIG. 3, electrostatic charge can be inserted which generates an adhesion of the paper sheets among each other which is independent of the value of the friction of a paper sheet and can not cause undesired damages.

As is shown schematically in FIG. 3, the electrostatic charge is preferably contactless inserted into the stack of paper sheets and thereby preferably dosed in such a manner that a substantially predetermined number of paper sheets, preferably a partial stack 12 to be removed, or a remaining residual blank stack 11 of paper sheets are fixed. 

1. A control device for the removal of a partial stack from a stack of paper sheets, comprising: a. a camera (30) for generating a camera image; b. means (41) for generating of at least two substantially parallel light beams whose reflections (52, 53) are reproduced on a stack of pa-per sheets in the camera image (50); and c. means providing a control signal for the removal of a partial stack (12) using the distance (54) of the reflections (52, 53) in the camera image (50).
 2. The control device according to claim 1, wherein the light beams extend substantially parallel to the plane of the paper sheets.
 3. The control device according to claim 1, having a further light beam to determine the distance between the camera and the stack of paper sheets.
 4. The control device according to claim 3, wherein the third light beam is not parallel to the other light beams.
 5. An unstacking device, comprising a control device according to claim
 1. 6. The unstacking device according to claim 5, further comprising a device for fixing paper sheets, wherein the device comprises means for inserting of electrostatic charge (60) into the stack of paper sheets.
 7. The unstacking device according to claim 6, wherein the means for insert-ing of electrostatic charge (60) are formed so that a partial stack of paper sheets, in particular a partial stack (12) of paper sheets to be removed, or a remaining residual blank stack (11) are fixed.
 8. The unstacking device according to claim 5, further comprising a parting mechanism (20) with a parting knife (21).
 9. The unstacking device according to claim 8, wherein the parting knife is formed so that it can be swivelled downward.
 10. The unstacking device according to claim 9, wherein the parting knife (21) can be swivelled downward by an angle a so that it is substantially parallel to the lower side of the partial stack which contacts the parting knife.
 11. The unstacking device according to claim 8, further compris-ing a lifting device for the stack of paper sheets which lowers the residual blank stack after a broaching with the parting knife (21).
 12. The unstacking device according to claim 11, wherein the lifting device is preferably servo-controlled and comprises highly precise ball spindles free of play.
 13. (canceled)
 14. (canceled) 